The present invention relates to a transfer system for multi-station presses and/or press working lines.
In for example, multi-station presses or press working lines, transfer systems have the task of transporting sheet metal parts or other workpieces from one press station to another. A workpiece passes successively through all press stations. The transfer system has the task of moving the opening tool over, i.e. below the top tool lifting off the workpiece, of picking up the workpiece, of moving it into the still open tool of the next press station and of depositing the workpiece there. Before the top tool is placed on the workpiece, the corresponding part of the transfer system must have been moved out of the tool.
During this operation, the gripper devices of the transfer system must cover considerable distances and move relatively large masses. Particularly with large-part presses, vehicle body presses and comparable facilities, very high accelerations and braking decelerations result and cannot easily be infinitely increased when the running speed (stroke number) of the press is to be raised.
EP 0388610 B1 describes a press facility which has a two-axis transfer system. The transfer system has two running rails which extend on both sides of the tools along the entire length of the press facility and on which travelling carriages are disposed. The running rails are connected with lifting devices which move the running rails synchronously up and down in the timing of the hybrid press facility. Two mutually opposite travelling carriages respectively are connected with one another by suction bridges or cross traverses. These are provided with vacuum suction devices so that a workpiece can be taken up and deposited in a controlled manner. By way of a transport linkage, the travelling carriages are connected with a drive to provide them with a longitudinal movement. By superimposing the lifting and lowering movement of the running rails on the longitudinal movement of the travelling carriages, the suction bridges negotiate the desired transfer curve by which the parts are transported.
When the tools close, the suction bridges must stand between the tools. Because of the finite moving and transporting speed of the suction bridges, this means that a maximal number of strokes cannot be exceeded. With smaller press strokes, higher stroke numbers are frequently desirable.
In addition, so-called three-axis transfer systems are known, in which, instead of the running rails, transfer bars are provided. In addition to the lifting and lowering movement, the transfer bars can also carry out a transfer movement in the transport direction and an opening and closing movement laterally with respect to the transport direction. The transfer bars carry blades which can reach laterally under the sheet metal parts.
Transfer systems of this type can carry out, for example, a return stroke when the tools of the individual press stations are closed. In the third axis, the blades held on the transfer bars carry out a lateral escape movement and move laterally past the closed tools. However, the blades grip the workpieces only on the edge. For this type of parts transport, the stability of the workpieces must therefore be sufficiently high. If parts are separated in a press station, i.e., if two sheet metal parts are cut out of a blank which are to be transported, e.g., side-by-side, the parts transport cannot be carried out only by means of the blades which reach into the tools from the sides. This limits the application possibilities of the three-axis transfer system.